A variety of services are provided via a network by use of computers. This type of service is exemplified by an online shopping site or a video hosting site. It is desirable in this type of service that a service interruption period disabling the service to be utilized is as short as possible. However, the service being provided is interrupted as the case may be due to a maintenance work exemplified by applying modification patch programs to an Operating System (OS) and various categories of applications or due to a hardware fault in operating the computer. Such being the case, a restraint of the service interruption involves taking a measure to redundantly configure the computers that provide the services. The redundantly-configured computers enable the services to be provided from another active computer even when one computer is stopped due to the maintenance.